1. Field of the Invention
The present invention relates to a character generating method and apparatus for developing an outline character, expressed by a logical coordinate system, on physical coordinates expressed by integer values.
2. Description of the Related Art
A printer, a display device or the like requires that character patterns be generated to print or display characters. In the generation of character patterns, recently, characters of various character sizes are demanded even for the same character. Therefore, the memory capacity increases if characters of various character sizes are given for the same character, particularly, for Kanji characters or the like which have many types of characters.
As a solution to this problem, an outline font system has been proposed. According to this system, data of character patterns whose contour lines are expressed in real numbers and also by a logical coordinate system, is provided, and this data is converted to a designated character size coordinate system to develop characters to a bit map image expressed by integer values.
It is demanded that characters should be restored to the original designs with high fidelity even after enlargement or reduction.
FIGS. 13A, 13B, 14A and 14B are explanatory diagrams of prior art.
Conventionally, in developing logical coordinate data expressed by real numbers, such as a figure or an outline font, to a bit map image expressed by integer values, a fractional portion of character data is rounded so that the data will be expressed in the units of pixels of a printer or a display. In order to express coordinate data by closest pixels, rounding is typically performed to count fractions of 5 and over as a whole number.
This will be explained with reference to Mincho Kanji characters "Mon" (meaning "gate") and "Nana" (meaning "seven") expressed in an outline form as shown in FIGS. 13A and 13B. The individual contour points which constitute the Mincho Kanji characters "Mon" and "Nana" are stored by integer logical coordinates like 1000.times.1000. Character outline data on the logical coordinates are converted to the necessary character size to have coordinate values including decimal points. If all the points are rounded to express the coordinate values by physical coordinates, all the points will be rounded to the nearest whole numbers.
When the outline data of those Kanji characters shown in FIGS. 13A and 13B are converted to the character size of, for example, 15.times.24 dots, the resultant Kanji characters becomes as shown in FIGS. 14A and 14B, respectively.
According to the prior art, the smaller the character point size becomes, the lower the character quality becomes so that any resultant character would have a poor appearance. This originates from a rounding error that occurs when the image of a character whose contour line is expressed by an equation is expressed by an integer coordinate system or physical coordinates. In particular, an oblique stroke or the like will have steps defined by vertical lines and horizontal lines, thus deteriorating the character quality. For instance, the Kanji character "Mon" in FIG. 14A has steps on vertical strokes on the right-hand and left-hand sides. Likewise, the Kanji character "Nana" in FIG. 14B has steps on top and bottom horizontal strokes.